Update Discord links

[baskrahmer]

What does this PR do?

Fixes #<issue_number>

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

---

📚 Documentation preview 📚: https://torchmetrics--2457.org.readthedocs.build/en/2457/

[codecov]

Codecov Report

Merging #2457 (d9adbf9) into master (b6fe6bb) will decrease coverage by 0%.
The diff coverage is n/a.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #2457   +/-   ##
======================================
- Coverage      69%     69%   -0%     
======================================
  Files         307     307           
  Lines       17357   17357           
======================================
- Hits        11957   11952    -5     
- Misses       5400    5405    +5